Hard disc drive cover-integrated gasket

ABSTRACT

A hard disc drive cover-integrated gasket, which comprises a metallic cover and a packing material integrated with the metallic cover, the packing material being a molding material from a mixture comprising 100 parts by weight of EPDM or a blend of EPDM and polystyrene type thermoplastic elastomer, 10-100 parts by weight of polypropylene type resin, 20-130 parts by weight of a plasticizer and 0.1-10 parts by weight of a cross-linking agent is easy to fabricate and has distinguished characteristics as low outgassing characteristics, low hardness, good sealability at elevated temperatures, etc.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a hard disc drive cover-integratedgasket, and more particularly to a hard disc drive cover-integratedgasket, which is easy to fabricate and has improved characteristics suchas low outgassing and good sealability.

2) Related Art

Recent tendency toward smaller sizes and higher performance ofelectronic appliances is requiring smaller and thinner structural parts,consequently giving rise to deterioration of assembling efficiency inthe fabrication process. To overcome such a problem, integration andcombination of parts are keenly desired, together with improvements intheir characteristics or performances such as outgassing, sealability,etc.

In electronic memory apparatuses, gaskets to be fitted to the hard discdrive cover particularly for preventing intrusion of water or dusts andfor satisfying low-outgassing requirements have been so far fitted tothe hard disc drive in the sandwich form of a single rubber sheet or afoamed polyurethane sheet between metallic covers of stainless steel,aluminum, etc. In this connection, it has been proposed to integrate ametallic cover of stainless steel, etc. with a rubber material such asfluoroelastomers, etc. by bonding with an adhesive, thereby improvingthe assembling efficiency (JP No. 2,517,797).

However, the proposed method is based on preparation of gasket-shapedrubber through an additional vulcanization molding step in advance,followed by bonding the rubber to a metallic cover with an adhesive,needing a prolonged series of process steps and complicating the processper se. Actually, the gasket vulcanization step needs a few minute, andthe vulcanized gaskets are liable to tear off to smaller pieces or arereadily susceptible to dust deposition thereon, etc., so repeatedwashing or screening is imperative before the assembling. Thus, a moresimplified method has been keenly desired.

To overcome the foregoing problems, it has been proposed to use a gasketmaterial comprising a polystyrene type block copolymer elastomer capableof simplifying the process step without a vulcanization step and alsocapable of material recycling to reduce the cost, as compared with theconventional rubber material (JP No. 2,961,068).

The proposed material is liable to become finer, softer and more sticky.Unless the material has been fixed by some means in advance, the workingefficiency will be lowered in the assembling work of hard disc drives.To overcome this problem, a gasket of polystyrene type block copolymerelastomer is prepared by injection molding into the so called frame inadvance, followed by inserting the framed gasket between a box and acover of hard disc drive to effect the desired integration. After all,additional parts such as frame, etc. are required in the proposedmethod.

Due to the recent tendency toward higher performance of hard disc drive,gaskets to be fitted to the hard disc drive covers are inevitablyexposed to elevated temperatures, e.g. 100° C. or higher. Thesepolystyrene type thermoplastic elastomers have failed to attainsatisfactory performance at such elevated temperatures.

Particularly, the gaskets to be fitted to the hard disc drive covershave strict requirements for sealability, cleanliness and heatresistance.

Three key factors that affect sealing characteristics are hardness,compression set characteristic and water permeability of the gasket.Hardness (JIS durometer type A) is preferably 60 or less. Gasket with ahardness of more than 60 fails to ensure sealing characteristic betweenthe hard disc drive and the cover due to clearances formed therebetweenby the bending backward force of the gasket, when fitted generally toassemble a hard disc drive product. Material with a poor compression setcharacteristic also fails to ensure sealing characteristics due totension loss in the course of long-term use, material with a compressionset of 100% or higher is impractical. Furthermore, water vapor(moisture) as well as dirt and dust etc. is included as an object to besealed, and thus the gasket materials must have a low waterpermeability. Involvement of water vapor inside the hard disc drive is acause for generating rusts.

Cleanliness-controlling factors are the following three: outgassing,components as contained and a filler which tends to drop off from thegasket. When the outgases generated from the materials deposit onto thedisc, such deposition will be a cause for crushing. Components ascontained in constituent materials, such as chlorine, silicon, sulfur,sulfuric acid, nitric acid, acrylate esters, etc. (including theirpresence in the form of ions) will also cause corrosion of hard discdrive interior. When a large amount of a filler having no affinitytoward the polymers is contained in the gasket materials, the fillerparticles have a high possibility of dropping off from the gasket tofall into the hard disc drive interior, giving also rise to crushing.

As is concerned with the heat resistance, the hard disc drives so farused in the personal computers, etc. are directed basically to indooruse, where the service conditions are at about 0°-about 60° C., ormaximum at about 80° C. even if used in continuous operation withinternal heat generation. When the hard disc drives are applied to carnavigators, etc., on the other hand, it is imperative that the hard discdrives mounted on cars can be immediately started even after being leftstanding in a cold area at low temperatures such as down to about −40°C., or can maintain their performance even after being left standing indirectly sun beam-irradiated, tightly closed car interior at elevatedtemperatures such as up to about 100° C. In the case of the polystyrenetype thermoplastic elastomer as the leading material up to now, glasstransition temperature (Tg) of the hard segment is about 100° C., andthus no better heat resistance is basically obtainable above about 100°C.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a gasket for hard discdrive, which is easy to fabricate and has distinguished characteristics,such as low outgassing, low hardness, good sealability at elevatedtemperatures, etc.

The object of the present invention can be attained by a hard disc drivecover-integrated gasket, which comprises a metallic cover and a packingmaterial integrated with the metallic cover, the packing material beinga molding material from a mixture comprising 100 parts by weight of EPDMor a blend of EPDM and a polystyrene type thermoplastic elastomer,10-100 parts by weight of polypropylene type resin, 20-130 parts byweight of a plasticizer and 0.1-10 parts by weight of a cross-linkingagent.

DETAILED DESCRIPTION OF THE INVENTION

EPDM is an ethylene-propylene-diene terpolymer elastomer, includingterpolymers with various diene monomers. EPDM can be formed intopolyolefin type thermoplastic elastomers as a blend type upon mechanicalblending with polypropylene type resin. Due to the presence of across-linking agent, EPDM can be also formed either into a partiallycross-linked blend type upon partial cross-linking of EPDM or into acompletely cross-linked blend type composite comprising a continuousphase of polypropylene and dispersed phases of completely cross-linkedEPDM.

Thus, polyolefin type thermoplastic elastomers can be formed from amixture of EPDM and polypropylene type resin (together with across-linking agent). In place of mixing these individual components,commercially available polyolefin type thermoplastic elastomers based onmixtures comprising these individual components in the above-mentionedproportions, for example, Mirastomer series of Mitsui Chemicalsproducts, Suntprene series of AES products, etc., can be used as such inthe present invention.

These polyolefin type thermoplastic elastomers have a distinguished heatresistance, because the softening temperature of polypropylene as a hardsegment is about 130°-about 150° C., and have good outgassing, butsomewhat higher hardness. To lower the hardness, the polyolefin typethermoplastic elastomers can be also used as a blend with a polystyrenetype thermoplastic elastomer.

As already described above, when the cover is fixed to a hard disc drivethrough a gasket of high hardness, the cover will be warped due to thebending backward force of the gasket, resulting in failure to effecttight sealing, whereas the gasket with too low hardness, e.g. 10 orless, will be very sticky or lose the mechanical strength, resulting ineasy tearing-off into smaller pieces. According to the gasketperformance, the bending backward force of the gasket will be lowered bymaking the gasket finer, whereby a gasket with a correspondingly higherhardness can be used.

From this point of view, a packing material with a hardness (JISdurometer type A) of 20-60, preferably 30-50, is desirable. That is,polyolefin type thermoplastic elastomer comprising 100-20% by weight ofEPDM as the main component and 0-80% by weight of polystyrene typethermoplastic elastomer, sum total being 100% by weight, can be used inthe present invention. In other words, polyolefin type thermoplasticelastomer only of EPDM or that of a blend of EPDM with a polystyrenetype thermoplastic elastomer can be used in the present invention. Thesetwo kinds of elastomers are nonpolar and are scarcely watervapor-permeable.

Particularly, polyolefin type thermoplastic elastomer comprising 100-50%by weight of EPDM as the main component has a remarkably improvedsealability in terms of compression set characteristic after the heattreatment at elevated temperatures such as about 80°-about 100° C.,whereas with increasing proportion of polystyrene type thermoplasticelastomer in the blend, the plasticizer retainability can be increasedto facilitate appropriate adjustment of hardness. In the case of singleuse of polystyrene type thermoplastic elastomer, on the other hand, thecompression set characteristic at elevated temperatures will bedeteriorated, and the long-term sealability cannot be maintained.

Polystyrene type thermoplastic elastomer for use in the presentinvention includes triblock copolymer [SEPS] ofpolystyrene-poly(ethylene-propylene)-polystyrene, triblock copolymer[SEEPS] of polystyrene-poly(ethylene/ethylene-propylene)-polystyrene,etc. SEPS can be obtained by hydrogenation ofpolystyrene-polyisoprene-postyrene block copolymer, whereas SEEPS can beobtained by hydrogenation of polystyrene(butadiene-isoprene) randomcopolymer-polystyrene block copolymer.

These polystyrene type thermoplastic elastomers preferably have a numberaverage molecular weight Mn of 50,000 or more. Below 50,000, bleeding ofthe plasticizer will be increased, and the compression set will be alsoincreased, resulting in such inconvenience as being practicallyunapplicable. The upper limit of the number average molecular weight Mnis not particularly limit but is usually about 400,000. Content ofamorphous styrene block of the polystyrene type thermoplastic elastomeris 10-70% by weight, preferably 15-60% by weight. Glass transitiontemperature (Tg) of the amorphous styrene block is 60° C. or higher,preferably 80° C. or higher. Polymer which connects both terminalamorphous styrene blocks is preferably amorphous. The polystyrene typethermoplastic elastomer to be contained in the polyolefin typethermoplastic elastomer can be used in a single species or in a mixtureof at least two species thereof. Actually, commercially available Septon2006 [SEPS] and Septon 4055 [SEEPS] can be used in the presentinvention, both of which are Kuraray's products to satisfy theaforementioned conditions.

Polypropylene type resin and plasticizer are selected in view ofmoldability and hardness of packing material, to be obtained by molding.Polypropylene type resin affects the moldability, whereas theplasticizer adjusts the hardness. On this ground, mixing proportions ofpolypropylene type resin and plasticizer must be appropriately selected.

Polypropylene type resin for use in the present invention includescrystalline polymers such as propylene homopolymer, copolymers ofpropylene with a small proportion of α-olefin (e.g. ethylene, 1-butene,1-hexene, 4-methyl-1-pentene, etc.). Polypropylene type resin is used ina proportion of 10-100 parts by weight, preferably 20-80 parts byweight, on the basis of 100 parts by weight of EPDM or a blend of theEPDM with the polystyrene type thermoplastic elastomer as the maincomponent of the polyolefin type thermoplastic elastomer. Above 100parts by weight of the polypropylene type resin, the resulting moldingproduct will have a higher hardness, whereas below 10 parts by weightthe resulting mixture will have a lower flowability, making injectionmolding hard to conduct.

Any plasticizer can be used without any particular restriction, so faras it can be used in the ordinary rubber or thermoplastic elastomers.The plasticizer for use in the present invention includes, for example,a petroleum-based softening agent such as process oil, lubricating oil,paraffin oil, etc., a fatty acid-based softening agent such as castoroil, linseed oil, rapeseed oil, coconut oil, etc., ester-basedplasticizer such as dibutyl phthalate, dioctyl phthalate, dioctyladipate, dioctyl sebacate, or the like, among which paraffin oil ispreferable. The plasticizer is used in a proportion of 10-130 parts byweight, preferably 50-120 parts by weight, on the basis of 100 parts byweight of EPDM or a blend of EPDM and polystyrene type thermoplasticelastomer. Above 130 parts by weight of the plasticizer, the resultingmolding product will have higher outgassing, whereas below 10 parts byweight the molding product will have a poor sealability.

As a cross-linking agent for use in the present invention, an organicperoxide, so far usually used as a cross-linking agent for EPDM, can beused in the case of using EPDM, and an organic peroxide can be alsopreferably used in the case of using a blend of EPDM and polystyrenetype thermoplastic elastomer. Thus, the organic peroxide for use in thepresent invention includes, for example, dicumyl peroxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, t-butylcumylperoxide, etc. The cross-linking agent is used in a proportion of 0.1-10parts by weight, preferably 1-5 parts by weight, on the basis of 100parts by weight of EPDM or a blend of EPDM and polystyrene typethermoplastic elastomer. The above-mentioned proportion is the commonlyused one.

The mixture comprising the foregoing individual components as essentialcomponents can contain, if necessary, further additives usually used inthe ordinary rubber or thermoplastic elastomers, for example, a powderysolid filler (such as various kinds of metal powder, glass powder,ceramic powder, granular or powdery polymer, etc.), an antioxidant (suchas amines and their derivatives, imidazoles, phenols and theirderivatives, etc.), waxes, a stabilizer, a tackifier, a mold releaseagent, a pigment, a flame retardant, a lubricant, etc.

To improve the wear resistance, moldability, etc. of the molding producta small proportion of thermoplastic resin or rubber can be further addedthereto. Still furthermore, to improve the mechanical strength andrigidity of the molding product, short-length fibers, etc. can be alsoadded thereto.

The mixture is melt kneaded by a heating kneader, such as a uniaxialextruder, a biaxial extruder, rolls, a Banbury mixer, a Brabender mixer,a kneader, a high-shearing mixer, etc. and, if further necessary, themixture can be admixed with a cross-linking aid, or these necessarycomponents are mixed together, followed by heat melting and kneading, ora thermoplastic material is prepared by kneading organic polymermaterials and the plasticizer in advance, and is used upon furthermixing with at least one organic polymer material of the same species asused above or different species.

The thus obtained thermoplastic elastomer compound, which comprises EPDMor a blend of EPDM and polystyrene type thermoplastic elastomer as themain component of polyolefin type thermoplastic elastomer, polypropylenetype resin, a plasticizer and a cross-linking agent, is injection moldedwith an adhesive-coated metallic cover as inserted into a mold, wherebythe compound can be molded into a gasket integrated with the metal coveras a packing material.

The metallic cover for use in the present invention is made from, forexample, an aluminum sheet, a galvanized aluminum sheet, a stainlesssteel sheet, a stainless steel damping sheet, or the like. The adhesivefor use in the present invention includes those obtained by graftingpolar groups of maleic anhydride, acrylic acid, etc. onto side chains ofpolyolefin type resin, thereby modifying the polyolefin type resin,followed by dissolution in an aromatic or aliphatic organic solvent tomake a liquid solution or a dispersion, or those obtained by dissolvingstyrene-butadiene copolymer elastomer in an aromatic or aliphaticorganic solvent to make a liquid solution, or the like. Without anyadhesive, the metallic cover is liable to peel off the resulting moldingproduct, resulting in failure of desired integrated molding. Theadhesive can be applied to the metallic cover by a most appropriatemethod selected from dipping application, spraying application, screenprinting, brush painting, stamping, etc.

By balancing the proportion of polypropylene type resin against that ofplasticizer in the aforementioned ranges, the hardness (JIS durometertype A) and the compression set (JIS K6262, 100° C. for 72 hours) of thegasket of the molded packing material can be adjusted to 20-60,preferably 20-50, and not more than 50%, respectively. When the hardnessexceeds 60, the bending backward force of the cover-integrated gasket,when fabricated by fitting the gasket to the hard disc drive cover, willbe large enough to cause deformation of the cover with the result ofincomplete sealing. That is, the gasket has a poor sealability. When thehardness is less than 20, on the other hand, the gasket will easily tearoff or will be sticky. Thus, careful handling must be made. When thecompression set exceeds 50%, no long-term sealability can be obtained atelevated temperatures. The shape of a packing material to be moldeddepends on the shape of a hard disc drive cover to be integratedtherewith.

The present hard disc drive cover-integrated gasket has distinguishedcharacteristics such as low hardness, good sealability at elevatedtemperatures, low outgassing, low water permeability, good adhesiveness,good moldability, etc. and thus can serve as an effective packingmaterial for hard disc drive cover. Particularly in the case of using,as the main constituent of the gasket molding, a polyolefin typethermoplastic elastomer comprising EPDM as the main component,distinguished sealability at elevated temperatures can be obtained, asgiven in terms of compression set values at elevated temperatures in thefollowing Examples.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples.

EXAMPLE 1

Parts by weight EPDM (Mitsui EPT 3045, Mitsui Chemicals product) 100Polypropylene type resin (J700GP, Idemitsu Kosan 25 product) Paraffinoil (Diana Process oil PW380, Idemitsu 100 Kosan product) Cross-linkingagent (Percumyl D, NOF product) 2

The foregoing components were injection molded into test sheets (150mm×150 mm×2 mm) by an injection molding machine (KM-80, made byKawaguchi Iron Works, Ltd.) at a set temperature: 210°-180° C.,injection speed: 0.5 sec., injection pressure: 100 MPa and cycle time:30 sec. The test sheets were used in tests of hardness, compression setat elevated temperatures, outgassing and water permeability. A piece ofcover-shaped aluminum sheet (electrolessly nickel plated to a thicknessof 2-5 μm) was coated with a modified olefin type resin adhesive (Skip#66, Sotec product) and inserted into a mold in advance, and theafore-mentioned same components were injection molded into the moldlikewise under conditions of injection speed: 0.5 sec., injectionpressure: 30 MPa and cycle time: 30 sec. to form a gasket integratedwith the cover piece. The resulting cover-integrated gasket was thensubjected to sealability test, adhesiveness test and moldabilityevaluation.

EXAMPLE 2

In Example 1, the amount of paraffin oil was changed to 120 parts byweight.

COMPARATIVE EXAMPLE 1

In Example 1, the same amount of polystyrene type thermoplasticelastomer (Septon 4055, a Kuraray product) was used in place of EPDM.

COMPARATIVE EXAMPLE 2

In Comparative Example 1, the amount of paraffin oil was changed to 120parts by weight.

Test sheets and cover-integrated gaskets obtained in Examples 1 and 2and Comparative Examples 1 and 2 were subjected to determination of thefollowing properties:

Hardness: according to JIS K6253 (a stack of three test sheets)Compression set test at elevated temperatures: according to JIS K6262;to determine percent compression set value at 100° C. for 72 hours

Outgassing test: a rectangular test sheet (50 mm×3 mm×2 mm) wassubjected to hot extraction at 120° C. for one hour and then subjectedto determination of outgassing amount. Outgassing amounts of less than50 μg/g are shown by ∘, and those of 50 μg/g or more by X in thefollowing Tables 1, 2 and 3. (Sheets with an outgassing amount of 50μg/g or more were evaluated as unpreferable for a gasket for hard discdrive cover requiring higher performance such as a server, etc.)

Water permeability test: 10 ml of distilled water was put into astainless steel (SUS) cylindrical vessel (inner diameter: 27 mm, depth50 mm), and a test sheet, shaped into a disc form (30 mm in diameter and1 mm in thickness) was placed on the open top of the cylindrical vesseland fixed with a concentrically hollow stainless steel cover disc(opening inner diameter: 27 mm). From the resulting data at 70° C. for100 hours were calculated water permeation coefficients (g·mm/cm²·24hrs). Coefficients of less than 5×10⁻³ (g·mm/cm²·24 hrs) are shown by ∘,and those of 5×10⁻³ (g·mm/cm²·24 hrs) or more by X in the followingTables 1, 2 and 3. (Sheets with a water permeation coefficient of 5×10⁻³or more were evaluated as unpreferable for a gasket for hard disc drivecover)

Sealability test: cover-integrated gasket was mounted onto an actualleak tester and subjected to heat treatment at 80° C. for 168 hours inthat state, and returned to room temperature. Then, a positive pressureof 5 kPa was continuously applied for 30 seconds from the inside of thetester. The gaskets without any leakage after 15 seconds are shown by ∘,and those with leakage by X in the following Tables 1, 2 and 3. (Leakagetook place when the gasket material had an inferior compressionset-characteristic or defects in the gasket shape)

Adhesiveness test: a perforated peel of the gasket, about 1 mm long, wasmade on the gasket adhesion side of a cover-integrated gasket, and astainless steel (SUS) wire was passed through the peel perforationportion, and a vertical tensile load was applied to the peel by the wirethrough the peel perforation portion to measure the load when the peellength was extended to about 10 mm. Those with a peeling load of 100 kPaor more are shown by ∘, and those with less than 100 kPa are shown by Xin the following Tables 1, 2 and 3. (Cover-integrated gaskets with apeeling load of 100 kPa or more had a satisfactory adhesiveness evenunder the actual service conditions)

Moldability evaluation: evaluation was made by visually observingmolding defects of product shape in the injection molding. That is,those without such defects as deformation, shrinkage, chipping, welds,short shot, flash, etc. or without defects in cover integrated moldingsare shown as 0, and those with such defects by X in the following Tables1, 2 and 3.

The results of the foregoing Examples and Comparative Examples are shownin the following Table 1. TABLE 1 Example Comp. Ex. 1 2 1 2 [Test sheet]Hardness (durometer type A) 50 40 45 40 Compression set at elevatedtemperatures (%) 43 40 44 41 Outgassing ◯ ◯ X X Water permeability ◯ ◯ ◯◯ [Gasket] Sealability ◯ ◯ X X Adhesiveness ◯ ◯ ◯ ◯ Moldability ◯ ◯ ◯ ◯

EXAMPLE 3

Parts by weight EPDM (EPT3045, Mitsui Chemicals product) 100 Polystyrenetype thermoplastic elastomer (Septon 2006, 50 Kuraray product [SEPS])Polypropylene type resin (J700GP) 25 Paraffin oil (Diana Process OilPW380) 100 Cross-linking agent (Percumyl D) 2

The foregoing components were mixed and extruded by a biaxial extruder(Hyper KTX46, made by Kobe Steel, Ltd.) at a temperature of 210°-180° C.and a revolution speed of 150 rpm to make compounds.

The resulting compounds were injection molded into test sheets (150mm×150 mm×2 mm) by an injection molding machine (KM-80, made byKawaguchi Iron Works, Ltd.) at a temperature: 210°-180° C., injectionspeed: 0.5 sec., injection pressure: 100 MPa and cycle time: 30 sec. Thetest sheets were used in tests of hardness, compression set at elevatedtemperatures, outgassing and water permeability. A piece of cover-shapedaluminum sheet (electrolessly nickel plated to a thickness of 2-5 μm)was coated with a modified olefin type resin adhesive (Skip #66, Sotecproduct), and inserted into a mold in advance, and the same compoundswere injection molded into the mold likewise under conditions ofinjection speed: 0.5 sec., injection pressure: 30 MPa and cycle time: 30sec. to form a gasket integrated with the cover piece. The resultingcover-integrated gasket was then subjected to sealability test,adhesiveness test and moldability evaluation.

EXAMPLE 4

In Example 3, the amount of EPDM was changed to 70 parts by weight, andthat of polystyrene type thermoplastic elastomer [SEPS] to 30 parts byweight.

EXAMPLE 5

In Example 3, the amount of EPDM was changed to 30 parts by weight, andthat of polystyrene type thermoplastic elastomer [SEPS] was changed to70 parts by weight.

EXAMPLE 6

In Example 3, the same amount of another polystyrene type thermoplasticelastomer (Septon 4055, Kuraray product [SEEPS]) was used in place ofthe polystyrene type thermoplastic elastomer [SEPS].

EXAMPLE 7

In Example 3, a styrene-butadiene copolymer elastomer-based adhesive(Diabond DA3188, Nogawa Chemical product) was used in place of themodified olefin type resin adhesive.

The test sheets and cover-integrated gaskets obtained in Examples 3 to 7were subjected to tests of hardness, compression set at elevatedtemperatures, outgassing, water permeability, sealability andadhesiveness, and moldability evaluation. In the sealability test,evaluation was carried out without heat treatment at 80° C. for 168hours. Results of the foregoing Examples 3 to 7 are shown in thefollowing Table 2. TABLE 2 Example 3 4 5 6 7 [Test sheet] Hardness(durometer type A) 45 48 40 46 40 Compression set at elevated 45 42 4745 45 temperatures (%) Outgassing ◯ ◯ ◯ ◯ ◯ Water permeability ◯ ◯ ◯ ◯ ◯[Gasket] Sealability ◯ ◯ ◯ ◯ ◯ Adhesiveness ◯ ◯ ◯ ◯ ◯ Moldability ◯ ◯ ◯◯ ◯

COMPARATIVE EXAMPLE 3

In Example 6, EPDM was not used, but the amount of polystyrene typethermoplastic elastomer [SEEPS] was changed to 100 parts by weight.

COMPARATIVE EXAMPLE 4

In Example 3, the amount of paraffin oil was changed to 5 parts byweight.

COMPARATIVE EXAMPLE 5

In Example 3, the amount of paraffin oil was changed to 150 parts byweight.

COMPARATIVE EXAMPLE 6

In Example 3, the amount of polypropylene type resin was changed to 5parts by weight.

COMPARATIVE EXAMPLE 7

In Example 3, the amount of polypropylene type resin was changed to 120parts by weight.

Results obtained in the foregoing Comparative Examples 3 to 7 are shownin the following Table 3. TABLE 3 Comparative Example 3 4 5 6 7 [Testsheet] Hardness (durometer type A) 44 74 28 39 86 Compression set atelevated 68 53 51 45 73 temperatures (%) Outgassing ◯ ◯ X ◯ ◯ Waterpermeability ◯ ◯ ◯ X ◯ [Gasket] Sealability ◯ X ◯ ◯ X Adhesiveness ◯ ◯ X◯ ◯ Moldability ◯ ◯ ◯ X ◯

1. A hard disc drive cover-integrated gasket, which comprises a metallic cover and a packing material integrated with the metallic cover, the packing material being a molding material from a mixture comprising 100 parts by weight of EPDM, 10-100 parts by weight of polypropylene type resin, 20-130 parts by weight of a plasticizer and 0.1-10 parts by weight of a cross-linking agent.
 2. A hard disc drive cover-integrated gasket according to claim 1, wherein the molding material from a mixture of EPDM, polypropylene type resin and cross-linking agent is a molding material of polyolefin type thermoplastic elastomer.
 3. A hard disc drive cover-integrated gasket, which comprises a metallic cover and a packing material integrated with the metallic cover, the packing material being a molding material from a mixture comprising 100 parts by weight of a blend of EPDM and polystyrene type thermoplastic elastomer, 10-150 parts by weight of polypropylene type resin, 20-130 parts by weight of a plasticizer and 0.1-10 parts by weight of a cross-linking agent.
 4. A hard disc drive cover-integrated gasket according to claim 3, wherein the blend comprises not less than 20% by weight of EPDM and not more than 80% by weight of polystyrene type thermoplastic elastomer.
 5. A hard disc drive cover-integrated gasket according to claim 1, wherein the plasticizer is paraffin oil.
 6. A hard disc drive cover-integrated gasket according to claim 3, wherein the plasticizer is paraffin oil.
 7. A hard disc drive cover-integrated gasket according to claim 3, wherein the polystyrene type thermoplastic elastomer is a polystyrene-poly(ethylene-propylene)-polystyrene block copolymer.
 8. A hard disc drive cover-integrated gasket according to claim 3, wherein the polystyrene type thermoplastic elastomer is a polystyrene-poly(ethylene/ethylene-propylene)-polystyrene block copolymer.
 9. A hard disc drive cover-integrated gasket according to claim 1, wherein the packing material has a hardness (JIS durometer type A) of 20-60 and a compression set value (JIS K6262, 100° C. for 72 hours) of not more than 50%.
 10. A hard disc drive cover-integrated gasket according to claim 3, wherein the packing material has a hardness (JIS durometer type A) of 20-60 and a compression set value (JIS K6262, 100° C. for 72 hours) of not more than 50%. 